Method drawAlpha

examples/scenes/src/BitmapScene.java:203–229

(Canvas canvas, IRect target, IRect screen, float dpi)

    public void drawAlpha(Canvas canvas, IRect target, IRect screen, float dpi) {
        try (var src = new Bitmap();
             var dst = new Bitmap();)
        {
            var srcInfo = ImageInfo.makeS32((int) (target.getWidth() * dpi), (int) (target.getHeight() / 2 * dpi), ColorAlphaType.UNPREMUL);
            src.allocPixels(srcInfo);
            int len = (int) (target.getWidth() / 2 * dpi);
            for (int x = 0; x < len; ++x) {
                int alpha = (int) (255f * x / len);
                int color = (alpha << 24) | (alpha << 16) | (0 << 8) | (255 - alpha);
                src.erase(color, IRect.makeXYWH(x, 0, 1, (int) (target.getHeight() / 2 * dpi)));
            }
            try (var image = Image.makeRasterFromBitmap(src.setImmutable());) {
                canvas.drawImageRect(image, Rect.makeXYWH(target.getLeft(), target.getTop(), target.getWidth(), target.getHeight() / 2));
            }

            if (src.extractAlpha(dst)) {
                try (var image = Image.makeRasterFromBitmap(dst.setImmutable());) {
                    canvas.drawImageRect(image, Rect.makeXYWH(target.getLeft(), target.getTop() + target.getHeight() / 2, target.getWidth(), target.getHeight() / 2));
                }
            }
        }

        try(var stroke = new Paint().setColor(0xFFE5E5E5).setMode(PaintMode.STROKE).setStrokeWidth(1);) {
            canvas.drawRect(target.toRect(), stroke);
        }
    }

    public void drawErase(Canvas canvas, IRect target, IRect screen, float dpi) {
        var w = target.getWidth() / 2;